There is currently a large domestic and international market for clean non-polluting generated grid and remote electrical power, such as the electrical power generated by solar energy generating systems. This demand is anticipated only to grow.
Terrestrial solar power systems typically are formed of flat panel photovoltaic (PV) cells, concentrator PV cell systems, or concentrator turbogenerators. Flat panel PV cell systems are advantageous in that they convert either direct or diffuse sunlight to electricity, though direct sunlight is preferred. The panels usually are stationary and the systems can become very large in order to generate sufficient amounts of electricity. Concentrator PV cell systems require fewer PV cells but can only convert direct sunlight to electricity, and therefore require a tracking system and clear skies. Concentrator turbogenerators use concentrated solar energy to heat a medium that is sent through a turbine to generate electricity.
One drawback in the implementation of each of these systems commercially is the expense associated with producing PV cells, tracking systems, and land costs. Moreover, solar power is not economically viable in cloudy regions such as the Northwestern United States or Northern Europe. Though solar power technically is feasible in these regions, the long intervals of low illumination a) drive a requirement for very large energy storage systems to provide power throughout the dark intervals, b) reduce the annual energy output per square meter of solar collection area, and c) do not allow use of concentrator PV cells during the frequent intervals of thin overcast. Thus, in regions of low illumination, solar power is effectively eliminated as a potential clean energy source.
Another market in which solar power is not currently economically feasible is in providing power for military forces, disaster relief, or other mobile applications that require infrastructure. Military forces typically consume large amounts of power, and they often use this power in locations where normal infrastructure either does not exist or is threatened by enemy forces. For example, the Department of Defense (DOD) recently-estimated that the actual cost for a gallon of fuel for the US Army in some parts of Iraq is $700 due to the cost of convoy security for tanker trucks or the cost of helicopter airlift of petroleum to remote locations.
Typical terrestrial power systems, such as dams, coal-fired generators, and terrestrial solar arrays, are immobile. These are unsuitable for use by military forces or emergency response agencies. Mobile terrestrial power systems typically rely on fossil fuels, e.g. diesel generators. Though these often are used by mobile forces, these power systems increase mobile forces' dependence on a steady supply of fuel, which comes at a great expense.
One suggested prior art solution for regions of low illumination is to use very large solar arrays and large energy storage systems. The large arrays produce excess power while the sun shines. This power charges the storage system. When sunlight is not available, the energy storage system is discharged to meet the need for power. Unfortunately, this solution is economically prohibitive as the internal rate of return on the large capital investment is too low for investors. The use of large energy storage adds to the cost of an already expensive system. As a result, this solution is not currently in use.
Another suggested prior art solution is to use solar power satellites (SPSs), also called space-based solar power (SBSP). This approach, proposed by Glaser in 1968 and studied extensively by researchers in the 1970's, uses extremely large satellites in geosynchronous earth orbit (GEO) to collect sunlight and transmit microwave energy to earth. Unlike sunlight, microwaves penetrate clouds, so power from SPSs is available despite cloud cover. But the initial engineering and transport costs are prohibitive. SPSs require transport of many thousands of tons of equipment to GEO for each satellite. Further, there are human safety concerns about irradiation by large side lobes of the microwave beam and environmental concerns about microwave heating of the ionosphere. Some recent studies suggest that SPSs could work in low earth orbit (LEO) where the side lobes would be smaller and less of the ionosphere would be penetrated by the beam. However, because LEO satellites spend more time in shadow and less time above a given receiver location, the duty cycle is much lower than in GEO, thereby reducing the rate of return on capital investments.
Moreover, typical SPS designs proposed using a gigantic 1 kilometer diameter transmitter with a microwave wavelength of about 12 cm—part of the spectral band set aside for industrial users. Assuming a diffraction-limited beam with uniform intensity across the aperture, the beam's half-width to the first null is about 0.15 milliradians. Achieving a beam this narrow requires exceptionally tight control of the transmitter's shape. Nonetheless, given the nearly 40,000 kilometers from GEO to a receiver in Europe or North America, the sidelobes of the beam remain fairly strong dozens of kilometers from the receiver. In addition to the increased amount of real estate, this raises human health concerns.
For the reasons discussed above, most cloudy regions in the world today have no plans to use solar power to meet their energy needs. However, most other energy options fail to meet increasing consumer (or regulatory) demand for environmental stewardship. Nuclear energy remains costly and, in many nations, politically sensitive. Most viable hydroelectric sites are already in use; furthermore, the environmental cost of hydroelectric power is increasingly recognized, resulting in some dams being torn down. Wind energy is economically and politically viable in some areas, but is not sufficiently available in many regions. Fossil fuels like petroleum or coal are becoming more costly and are implicated in global warming; petroleum is also subject to political embargoes or to attacks on oil fields, pipelines, ports, refineries, roads, or tanker ships (cf., the military costs for fuel in Iraq today.)